A phase change memory (PCM) is a new non-volatile memory that develops fastest currently, which stores corresponding data using different resistance values that a phase change material represents in a crystalline state and in an amorphous state, and is widely applied to compact discs (CD) and digital versatile discs (DVD). Research on high-density storage of the phase change memory is particularly important to adapt to requirements for massive information storage. Traditional methods for implementing a high-density phase change memory include: reducing an area of a phase change unit and reducing an area of a peripheral circuit. The former needs to improve a device structure and is limited by a photoetching size, and the latter needs to optimize design of an integrated circuit.
To overcome the foregoing problem, a multi-valued storage technology emerges. The multi-valued storage technology, different from a traditional binary storage method, can store at-least-two-bit data on a storage unit by fully using a difference between a resistance of a phase change material in a crystalline state and that in an amorphous state. In the prior art, a method for implementing multi-valued storage of a phase change memory generally includes: an erase process (or SET) and a write process (or RESET). The erase process is applying a pulse having a low amplitude and a long pulse width to a storage unit of the phase change memory so that the storage unit changes to a stable low-resistance crystalline state. The write process is applying a pulse having a high amplitude and a narrow pulse width to the storage unit so that the storage unit changes to a high-resistance amorphous state. Because a resistance value of the storage unit of the phase change memory changes according to a width and an amplitude of an applied programmed pulse, amorphous states having different resistance values can be implemented by applying single pulses having different amplitudes and different pulse widths to the storage unit. The amorphous states having different resistance values correspond to different storage states, thereby implementing multi-valued storage of the phase change memory.
The prior art uses a single pulse having a high amplitude and a narrow pulse width to implement multi-valued storage. However, when a single pulse having a high amplitude and a narrow pulse width is applied to a storage unit of a phase change memory, a temperature of the storage unit rises excessively fast, causing a thermal crosstalk problem